This is a testharness.js-based test.
[FAIL] Constructing sheet with custom base URL ueses that URL for CSS rules
assert_equals: expected "url(\\"http://web-platform.test:8001/custom/path/example.png\\")" but got "url(\\"http://web-platform.test:8001/css/cssom/example.png\\")"
[FAIL] Constructing sheet with relative URL adds to the constructor document's base URL
assert_equals: expected "url(\\"http://web-platform.test:8001/css/cssom/custom/path/example.png\\")" but got "url(\\"http://web-platform.test:8001/css/cssom/example.png\\")"
[FAIL] Constructing sheet with invalid base URL throws a NotAllowedError
assert_throws_dom: function "() => { new CSSStyleSheet({ baseURL: "https://test:test/"}) }" did not throw
Harness: the test ran to completion.